Process of reducing metallic oxides



Jan. 12, 9 G. D. mu. 2,307,997

PROCESS OF REDUCING METALLIC OXIDES Fiied April 11, 1942 aadon 3J0 WGJ/ amen/5Q ATTORNEYS Patented Jan. 12, 1943 UNITED STATES PATENT. OFFICE raocnss or REDUCING METALLIC oxmns Gilbert 1). pm, Mount Lebanon, r...

Application April 11, 1942, Serial No. 438,587

' 6 Claims. (01. 75-26) This invention relates to the direct reduction of metallic oxides, such for example as the oxides of iron, by the use of reducing agents which are comprised of or include hydrocarbons.

Attempts have been made heretofore to employ hydrocarbons as reducing agents without first converting the hydrocarbons into carbon monoxide and hydrogen. These attemps have not been attended with much success for the reason that in the arrangements heretofore provided for their utilization as reducing agents the hydro-' carbons do not get hot enough in the reducing operation to break up into hydrogen and carbon but to a considerable extent pass up the stack unaltered. Hydrocarbons in themselves are not very active reducing agents.

Since the breaking up of hydrocarbons into carbon monoxide and hydrogen is an endothermic reaction, it will be seen that if this reaction takes place in the reducing zone, when treating iron oxide, for example, it tends to produce a thermal condition interfering with the reduction operation. If it be attempted to apply the heat for this reaction, as well as for the reduction reaction, by external heating means, the amount of heat required to be conducted through the walls of the reaction chamber may produce zones of excessive heat, causing local melting or sintering of the oxides which will not only interfere with the reduction operation but will usually clog the reduction apparatus.

Attempts to preheat the hydrocarbons to the desired temperature to insure the desired heat the superheated vapors of hydrocarbon oils as well as hydrocarbons in a normally gaseous state.

A further object of the invention is to insure association of the ore or oxide and the reducing agent for a suflicient length of time for complete removal of the oxygen. Still another object of the invention is to insure such intimate contact of the material to be reduced and the reducing agent that the necessary reaction will take place.

The invention furthermore aims to provide a reduction process, in which hydrocarbon reducing agents may be employed, which can be practiced I continuously.

It is well known that when iron oxides, either of the formula FeaO: or of the formula Fes04, are

caused to be intimately mixed with carbon and hydrogen, at elevated temperatures, the carbon and the hydrogen will unite with the oxygen in the oxide ore and form C0, C02, and HzO'and leave as a residual product pure iron, Fe. The

present invention, as hereinabove pointed out, aims to utilize hydrocarbons, containing the carbon andthe hydrogen combined, without first transforming them to bring the carbon and the hydrogen into the elemental state or even into the water gas form of hydrogen and carbon monoxide. I

More particularly, the invention aims to take iron oxide or other metallic oxide, after it has been prepared mechanically to expose the greatest possible surface, and contact it with a gasified hydrocarbon or a superheated vaporized hydrocarbon oil at temperatures above those at which claimed in my co-pending application Serial No.

337,115, filed May 25, 1940, that hydrocarbon oils can be vaporized and raised to relatively high temperatures, above the known cracking temperatures, without carbon deposit, by the utilization of a high velocity circulatory system such as shown and described in said application. In the vaporizing and superheating apparatus described and claimed in my co-pending application, de-

, particularly to make possible the utilization of posit of carbon in the heating coils is prevented and also' prevents the formation of zones in the stream where there is no liquid and in which overheating of the tubes can take place. In this apparatus it will be seen that a very high state of turbulence is maintained in the tubes throughout the travel of the mixed streamof vapor and liquid through the tubes and that this'state of turbulence, with the high velocity flow, insures a uniform wetting of the tubes, a wiping action that removes carbon deposit and an avoidance of local overheating which tends to prevent the carbon deposit in the first place.

In practicing the novel process of the present invention, which will now be described in its application to the reduction of oxides of iron, although it is to be understood that it is equally applicable to they reduction of other metallic oxides, the iron ore to be reduced will first be' crushed to that degree of fineness necessary for removal of the gangue .to the desired degree, which in most cases will be from 60 mesh up "to 100 mesh or even finer, depending upon the character of the ore. The crushed ore will then be treated to separate the oxide from the gangue or impurities, after which treatment the resultant concentrate will consist mainly of FeaOa or Fe3O4.

After concentration the powdered ore is thoroughly heated and brought to the desired reduction temperature, which will be below the melting point of the iron and any still retained impurities. For best results this temperature should be between 1200 F. and 2000 F., and preferably will be at least 1500 F. At this temperature the heated ore is brought into intimate association with the gasified or superheated vaporized hydrocarbon which has been preheated, preferably to substantially the same temperature asthe ore. This superheating of the vaporized hydrocarbon can be effected, as above pointed out, in the vaporizing and superheating apparatus of my co=- pending application hereinabove identified.

In order to insure the intimate association of the heated ore and the heated hydrocarbon essential to cause the reduction reaction to take place and in order to maintain this association sufficiently long'to completethe reduction, it has been found advantageous to employ special apparatus such as that disclosed in my application for U. S. Letters Patent Serial No. 341,478, filed June 20, 1940, which is a continuation in part of my application Serial No. 244,612, filed December 8, 1938. In the types of apparatus set forth in the applications for Letters Patent just referred to, turbulence is set up in the fluid stream by causing it to pass in succession through zones 'of higher than average velocity and lower than average pressure and of lower than average velocity and higher than average pressure. In this apparatus the heated oxide may be caused to partake of the turbulent movements of the superheated hydrocarbon vapor or gas thus insuring not only an intimate commingling of the hydrocarbon with the oxide, but a commingling of the particles of the oxide with each other. The a pparatus thus brings about both a reaction between the fluid and the solid and a rubbing action between the oxide particles themselves. In the apparatus described in said applications, provision is also made for selective recyling of the particles whereby those requiring more extended treatment will .receive such treatment.

The operation of the apparatus of my co-pending applications can be so governed and the temperatures therein so maintained that the commingled particles of'ore and vapor will remain in their interactive and reactive relation to each other for a definite period of time, and at more or less definite temperature and pressure, to insure the desired complete reduction. During this reducing process a further separation of the metallic oxide from the gangue will take place because of the fracturing or degradation due to the high temperatures and due to the impinging effect upon the particles as they are driven against the bailles of the apparatus of said co-pending applications and, to some extent, against each other.

At the end of the period of reaction and interaction in the reactor, the mixture of iron and residual gases, and possibly some residual vapor, will be passed into dry collectors or other separators such as are well known and in general usefor separating finely divided solids from fluids where the solid Fe will be separated from the residual gases and/or vapors and from any gangue that may have been separated from the oxide in the reaction chamber. The substantially pure iron or other metal can then be consolidated, shaped and formed by extrusion, compression, roiling or forging into finished products and preferably in such manner as to make use of the residual heat of the reduction operation.

The residual gases can be used as a source of fuel to supply the necessary heat involved in the various operations, such as the preheating of the oxide and the hydrocarbon. It will. be understood that a preheating of the oxide and of the hydrocarbon to temperatures somewhat above the temperature required for the reduction reaction may be desirable to provide heat-to supply that lost in the breaking up of the hydrocarbon into its elements and to supply any deficiency due to the endothermic hydrogen and carbon re-,

duction reactions. Additional heat to compensate for the endothermic reactions may be supplied by heating the reaction chamber by external heating means, being careful, of course, not to raise it to a temperature at which melting of any of the impurities still in the ore might take place.

Referring now to the drawing which illustrates apparatus suitable for carrying out the process, this apparatus combining the apparatus illustrated in my co-pending applications Serial Nos. 341,478 and 337,115, hereinabove identified, the hydrocarbon, to be converted into a superheated vapor havlng more or less the characteristics of a fixed gas, is treated in the apparatus shown at the left of the figure, this apparatus comprising a heating chamber or furnace 2 provided with burners 4 located in the refractory support 5. The flame from each burner projects into the central combustion space 8 bounded by the refractory and also extends somewhat up into the combustion space III which is bounded by the inner coil l2 of the tube in which the heating of the hydrocarbon is effected and through which it circulates. The outer coil l4, although located in the heating chamber 2, is shielded from the radiant heat of the fiame by the inner coil I2 which is a continuation of the outer coil I4, These coils may rest upon and be partly supported by the refractory 6. The prod iligts of combustion pass out through the stack As shown in the drawing, the hydrocarbon oil to be vaporized and superheated passes through the outer coil l4 before it enters the inner coil I 2 in the heating chamber, the outer coil I4 having an extension l8 outside the chamber 2 into which the hydrocarbon oil is forced by a pump 28 that receives it from a storage or supply tank 22. The oil, after it has passed through the outer coil I4 and through the inner coil l2 and has been vaporized and superheated, passes out of the heating chamber through the extension 24 of the inner coil l4. The extension 24 has two branches, one of which, 28, conducts the vaporized and superheated hydrocarbon to the point of use, for example, to the reaction apparatus shown which is of the type disclosed in my copending application Serial No. 341,478, filed June 20, 1940. The other branch 28 constitutes a bypass connecting the output extension 24 of the inner coil 12 with the input extension l8 of the outer coil l4. Located in the bY-DM 28 is'a valve 88 for controlling the amount of superheated vapor to be by-passed from the output extension 24 into the input extension l8 and also the pressure drop through the by-pass. If additional pressure drop is desired the by-pass 28 may connect with a venturi 28 in the input l4,

as shown; The venturi also contributes to setting up of turbulence in the combined stream of vapor and liquid.

By providing the by-pass 28, together with its control valve 88, a part of the vaporized and superheated hydrocarbon may be introducedinto the liquid hydrocarbon which is being forced into the outer coil l4 through its extension l8 by the action of the pump 28. The superheated vapor is introduced in a sufllcient amount in respect to its contained heat, so that it will not be condensed in the liquid but will sweep along'with the liquid hydrocarbon, as it enters the outer coil 14, a

as a combined stream of vapor and liquid. The vapor and liquid will sweep through the coil l4 together, the liquid being in a sense entrained in the vapor stream, a result growing out 01 its rapid flow. It will be seen that the pressure built up by the vaporization of the hydrocarbon in the coils l2 and i4, and particularly in the coil l2, will provide the desired pressure drop for obtaining the desired velocity of flow of the vaporized hydrocarbon through the by-pass 28 and the outer coil l4 as well as through the inner coil I2.

In this manner a relatively high velocity of flow may be maintained of the combined stream of liquid and vapor and a very high degree of duced may be contained in a hopper, shown conventionally at 34, and which may be heated in any suitable manner to provide for preheating of the ore or which may hold ore preheated before it is introduced into the hopper, connected by any suitable conduit 88 with an injection chamber 38 into which the pipe 28 from the superheater extends, this pipe 28 being provided at its end within the chamber 38 with a nozzle 48 through which the superheated vapor is discharged into the narrow upper part of the cham- It will.

duction is to take place, hereinafter referred to as reaction chambers, are'enclosed within a cylindrical side wall 44 and top and bottom walls 48 and 48. As shown, the entire casing may be enclosed within an insulating cover 58 and may be provided with any suitable heating means as, for example, electric resistance wires 52.

The straight section of tubing 42, constituting the upper part of the housing in which the chamber 88 is located, has connected to-its upper end one section 84 of a venturi, the section 84 7 having a comparatively steeply tapering interior passage 58 to produce the desired increase in velocity and reduction in pressure of the inflow- The outer face 58 of the upper end of the section 54 is also conical and tapers to meet the interior passage 58 in a comparatively sharp edge 88, the tapered upper end of the section 54 extending through the bottom of an inverted frusto-conical partition or baille 82 in the casing 44 which forms the bottom of the reaction chamber 84 and serves as a hopper-like structure to direct the fluid and-any entrained solid-to be recirculated to the low pressure part of the venturi, more fully to be described hereinafter. Positioned above the upper end of the section 54 of the venturi is a section 88 in which is formed the expansion end of the venturi, the section 88 having at its lower end a bell-mounted opening 88 of an internal conical taper substantially corresponding to the external conical taper of the outer face 58 of the section 54 and being Fromthe foregoing description it will be seen I that the superheated hydrocarbon vapor entering the tube 42 from the jet 48 and flowing under a substantially uniform flow-impelling pressure will, as it is forced through the contracting pas sage 58 in the section 54, travel under the well known law of the flow of fluids at. an increased velocity and at a reduced pressurethrough the upper end of the passage 58 and will be projected into the bell mouth 88 in the section 88 at this increased velocity. There will thus be in the conflned flow of the fluid a region of low pressure with which the annular passage 18 commu'nicates, thus creating a suction tending to draw the surrounding fluid into this passage for recirculation together with any finely-divided ore or other solid that may be entrained in the fluid.

Spacer bars 14 support a second frusto-conical partition member 18 in such position as to divide the space within the casing 44 into twochambers, the partition member 18 supporting a. second venturi comprising a member 18 of an internal and external construction similar to the member 54 and another member 88 of an internal and external construction similar to the member 88 of the lower venturi.

Located above the expansion ends of the respective venturis are streamlined baiiles 82 .and 84, the baffle 82 being supported by three brace members 88 connected at their upper ends to the baiile 82 and'at their lower ends to the inner face of the partition member 88 and the baflle 84 being supported by similar brace members 88. The venturi sections 88 and 88 are also shown as supported in their proper relations to the sections 54 and I8 by connections to the respective sets of brace members 86 and 88.

From the foregoing description, it will be seen that the superheated hydrocarbon, withits entrained finely divided ore, as it enters the reaction chamber 64 through the passage 12 in the upper part of the lower venturi will travel from a zone of high velocity and reduced pressure to a zone of low velocity and higher pressure and at the same time the stream of mixed superheated vapor and finely divided ore will strike against the blunt end of the streamlined baflle 82. A partoi the stream, following the streamlining oi. the baiiie 82, will go on into the passage in the lower member 18 of the upper venturi while a part will be directed toward the side wall of the lower chamber 64 and will return downward and enter the passage Ill into the low pressure part of the lower venturi. There is thus brought about both a marked turbulence in the stream insuring intimate reaction between the reducing agent and the ore and a recycling of the particles usually the larger particles needing more extensive treatment, with the result that the reduction is usually substantially completed before the mixed stream of superheated hydrofluid hydrocarbon is preheated to substantially carbon and finely divided ore enters the upper venturi. If, however, the reduction has not been completed in the lower chamber, it will doubtless be completed in the upper chamber 90 where the same action and recycling takes place; The reduced ore is carried out together with the gaseous products of the reduction through the discharge pipe 92.

From the foregoing description it will be seen that by the process of the present invention the possibility of using hydrocarbons as reducing agents, without first breaking them up into their constituent elements or even using them to form water gas, has been realized and that in this manner the direct reduction of metallic oxides can bebrought about with a comparatively economical use of hydrocarbons, in fact, a much more economical use of the hydrocarbons than by any prior method of employing hydrocarbons for reduction purposes of which Iam aware.

This application is a continuation input of my application Serial No. 335,764, filed May 1'7, 1940, for Process of reducing metallic oxides.

What is claimed as new is:

1. That improvement in the 'art of reducing metallic oxides, which consists in heating the oxide, in a concentrated and finely dividedcondition, to a temperature in the reduction range and also above that at which CO readily decomposes but below the melting. point of the metal, preheating a fluid hydrocarbon to substantially the same temperature, by forcing said hydrocarbon at high velocity through a zone of superheat and accelerating its velocity and insuring turbulence by reintroducing into the stream of hydrocarbon entering the superheating zone a portion of the hydrocarbon leaving the superheating zone, effecting an entrainment of the heated finely divided oxide in the heated hydrocarbon fluid and its intimate association therewith and maintaining the oxide and hydrocarbon fluid in such intimate association and at reduction temperature until the reduction is completed.

2. A process according to claim 1, in which the finely divided oxide is preheated to a temperature between 1200" F. and 2000 F. and in which the the same temperature.

3. A process according to claim 1, in which separation of the reduced iron from the fluids with which it is commingled is efiected while the iron stillretains at least some of the heat from the reducing zone.

4. A process according to claim 1, in which the hydrocarbon fluid is brought into-a turbulent condition and the oxide is caused to partake of the turbulent movements of the fluid.

5. A. process according to claim 1, in which provision of suflicient excess heat is made in the preheating of the oxide and. of the hydrocarbon fluid to compensate for consumption of heat incidental to the decomposition of the hydrocarbon fluid during the reduction reaction.

6. A process according to claim 1, in which heat is also conducted to the reduction zone to replace that consumed by the endothermic reactions which take place there.

GILBERT D. DILL. 

